On 6 July 2010, Prime Minister David Cameron appointed Gibson to head the Detainee Inquiry, which would look into allegations that the UK intelligence services were complicit in the torture of detainees, including those from the Guantanamo Bay detention camp or subject to rendition flights.[8][9] Troubled from the outset[10]—Gibson's appointment was questioned by the director of Reprieve, Clive Stafford Smith, almost as soon as it was announced,[11] and human and civil rights and other advocacy groups slammed the inquiry for its lack of independence, impartiality, openness, and its failure to meet the UK's stringent obligations under domestic and international law to comprehensively investigate claims of torture (some groups had such grave misgivings that they threatened to boycott it)[12]—the Detainee Inquiry was eventually scrapped after it reportedly fell into conflict with police investigations.[13]

After a much-criticised delay,[14][15] the interim report of the Inquiry was finally published on 19 December 2013. It concluded that the British intelligence services had been complicit in extraordinary rendition.[16] It was announced that further investigations would be undertaken by the Parliamentary Intelligence and Security Committee.[17]

^"Intelligence Services Commissioner" (Written Statements, 20 March 2006). Lords Hansard, Session 2005–06, Volume 680, Part 122, Column WS18. Retrieved 9 June 2013. The Lord President of the Council (Baroness Amos): I am pleased to announce that my right honourable friend the Prime Minister (Tony Blair) has approved the appointment of the right honourable Sir Peter Gibson as Intelligence Services Commissioner under the terms of Section 59 of the Regulation of Investigatory Powers Act 2000. The appointment will commence on 1 April 2006 and will run for three years.

^"Treatment of Detainees" (House of Commons Debates, 6 July 2010). Commons Hansard, Session 2010–12, Volume 513, Part 27, Column 176. Retrieved 9 June 2013. "The Prime Minister (Mr David Cameron): While there is no evidence that any British officer was directly engaged in torture in the aftermath of 9/11, there are questions over the degree to which British officers were working with foreign security services who were treating detainees in ways they should not have done. […] So we will have a single, authoritative examination of all these issues. […] It will look at whether Britain was implicated in the improper treatment of detainees, held by other countries, that may have occurred in the aftermath of 9/11. […] I have asked the right hon. Sir Peter Gibson […] to lead the inquiry." The other members of the three-member inquiry team were Janet Paraskeva and Peter Riddell.

^"Intelligence Services Commissioner" (Written Statements, 20 January 2011). Commons Hansard, Session 2010–12, Volume 521, Part 102, Column 54WS. Retrieved 9 June 2013. The Prime Minister (Mr David Cameron): In accordance with section 59 of the regulation of Investigatory Powers Act 2000, I have agreed to appoint the right hon. Sir Mark Waller as Intelligence Services Commissioner from 1 January 2011 to 31 December 2013.

^"About the Inquiry". Official website of the Detainee Inquiry. Retrieved 9 June 2013. The Inquiry has been referred to by different names including the 'Gibson Inquiry' and the UK 'Torture Inquiry', its official title is The Detainee Inquiry.